1. Technical Field
The embodiments of the present disclosure relate to wireless communications and, more particularly, to a calibration technique to be applied to wireless receivers that receive transmissions of multiple carrier signals in down link communications.
2. Description of Related Art
In the mobile communication area, various systems are being implemented throughout the world to increase the amount of voice and data traffic that can be carried over the air to wireless devices. These systems include universal mobile telecommunications system (UMTS), advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), Enhanced Data rates for GSM Evolution (EDGE), General Packet Radio Service (GPRS), as well as others. One recent development is Long Term Evolution (LTE), which uses a standard developed under the 3rd Generation Partnership Project (3GPP or 3G) and is marketed as 4G communications technology.
As more constraints are placed on mobile network operators to provide improved data throughput and quality of services, new techniques are constantly being sought to provide such improvements or new developments. Network operators are looking to offer more attractive and distinctive services to enhance the end user experience, while device (e.g. phone) manufacturers and chipset vendors are competing to create highly desirable mobile devices and applications. One way to achieve an increase in downstream data rates is to increase the bandwidth of the down link communication.
One recent technique is the use of multiple transmission paths between a transmitter and a receiver. Commonly referred to as Multiple-Input/Multiple-Out (MIMO) communications, substantially simultaneous transmissions of data over multiple paths permit more data throughput between two or more devices. Typically in a MIMO device, multiple antennas are employed to transmit and receive multiple channels. Time and/or spatial diversity (including antenna diversity) may be employed to obtain the MIMO transmission. However, for MIMO transmitters, the radio front end typically requires multiple transmission paths and associated components to transmit multiple channels simultaneously. Likewise, for a MIMO receiver, the radio front end also requires multiple receiving paths and associated components to receive multiple channels simultaneously.
Furthermore, a new technique is currently being developed utilizing the LTE standard, in which the down link bandwidth is increased via so-called carrier aggregation. For example, Release 10 under the current LTE standard and in a move toward the LTE-Advanced standard, specifies that radio frequency (RF) carriers from one or multiple base stations (Node B) may be aggregated and jointly used for transmissions to/from a single terminal. That is, instead of a single RF carrier being transmitted from a node (such as a cell tower, Node B, etc.) to a mobile device, the new LTE standard allows multiple carriers from one or multiple nodes to be sent down link to a single terminal. Because the use of multiple carriers increases the bandwidth of the transmitted signal, down link data rates to a user terminal or user equipment (UE) may be increased as well using this technique.
For a multi-path receiver receiving multiple carriers, significantly more components are now present in a radio receiver for receiving and processing multiple carriers. A self-calibration routine in a radio receiver is now further complicated by the presence of multiple processing paths in the receiver. Although these complexities in calibration may be dealt with at the factory during initial factory calibration, a self-calibration technique in the field during actual usage of the radio device (e.g. use by a consumer) usually relies on on-chip circuitry and routines present in the device. Whereas a single calibration circuitry may be employed in single path receivers, such circuitry, if duplicated for each path in a multiple carrier receiver, may present significant additional constraints that may be undesirable.
Accordingly, one solution is to find a more robust and/or efficient self-calibration technique to be implemented for multiple carrier receivers.